An image forming apparatus is usually provided with a light source, which emits a light beam through a rotatable polyhedron deflector onto a surface of a photoconductor to form a latent image thereon. The light beam emitted by the light source passes an optical scanning system such as a f-theta lens before it reaches the surface of the photoconductor. As the light beam passes the optical scanning system, the light level of the light beam may change according to the image height of the f-theta lens, thus resulting in the fluctuations in density of the latent image to be formed.
In order to solve this problem, the light level of the light beam to be emitted by the light source is controlled based on the light level of the light beam that reaches the surface of the photoconductor, for example, as described in the Japanese Patent Application Publication No. H06-255172. This approach, however, requires a light level detection sensor capable of detecting the light level of the light beam at the surface of the photoconductor, and an additional control circuit to control the light level of the light beam based on the detection result of the light level detection sensor.
The other approach for solving the above-described problem is to control the light level of the light beam based on shading correction data previously stored in a memory. For example, as described in the Japanese Patent Application Publication No. 2000-71510, using the shading correction data, the light level of the light beam to be emitted by the light source may be adjusted based on a specific position at which the light beam is to be scanned. This approach, however, requires a sufficient memory space as a sufficient number of shading correction values are needed to obtain a smooth shading correction curve.